Low-Cost Nanomaterials for High-Performance Polymer Electrolyte Fuel Cells (PEMFCs) - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 360

A large number of reports are available on preparing CNT-based electrodes
especially to increase the Pt utilization by means of using different preparation
conditions such as chemical reduction in a formaldehyde bath and electrochemical
deposition of Pt on CNTs. Growing CNTs directly on the carbon paper support in
order to reduce the ohmic resistance, and the modification of the reduction method
to prepare smaller nanoparticles with narrow distribution on size have also been
reported as an interesting alternative for Vulcan XC-72-based electrodes. Even
though such type of CNT-based electrodes demonstrating performance better than
that of Vulcan XC-72-based electrodes but their durability and chemical stability
aspects need to be rigorously evaluated [ 66 - 75 ].
5.4 Nitrogen-Doped CNTs as ORR Catalysts to Replace Pt
Even though Pt is used currently as the benchmark catalyst for ORR, it has to be
ultimately eliminated from the catalyst layer considering the very low abundance
of Pt on the earth crust (3.7 9 10 -6 %) and its fluctuating cost [ 76 ]. Interestingly,
N 2 -doped CNTs tend to give an option here although at present, it is only a partial
solution waiting for confirmation from results of durability studies [ 77 - 82 ]. For
example, vertically aligned CNTs containing nitrogen have been reported to show
better ORR catalytic activity than that of Pt as proved by the cyclic voltammetry
and RRDE experiments. Despite the fact that these results are in alkaline medium,
the possibility of N 2 -doped CNTs as a better support materials for Pt electrocat-
alysts on the cathode and anode of PEMFCs is really tempting where some of the
degradation issues can be prevented due to robust mechanical properties of CNTs
[ 79 ]. More promising results on N 2 - and B-doped CNTs are expected to revolu-
tionize this area in the near future.
5.5 Use of CNTs as Anode Support
Compared to the vast number of reports available on cathode support materials,
only a few reports are available for anode supports mainly due to the highly facile
nature of the hydrogen oxidation reaction and less critical materials requirements.
However, the actual challenge in the anode is to obtain sustained performance
using reformed H 2 having considerable CO content. In this regard, catalyst sys-
tems (e.g. Pt/Ru, Rh) that show good activity towards methanol oxidation reaction
are expected to have a better tolerance for CO and substantial efforts are rendered
towards improving the support metal interaction. Since stronger metal support
interactions (SMSI) would help the electron transfer between the metal and sup-
port during electrochemical reactions, Pt nanoparticles deposited on CNTs tend to
exhibit increased catalytic activity than that of unsupported metal due to the
unique electronic structure. Interesting improvements have been observed for